Electrical contacting element



De@ 6 1949 F. R. HENSEL ET AL l 2,490,214

ELECTRICAL CONTAC-'rma ELEMENT Filed July 19, 1945 5y @ua-FM,

ATTORNEY Patented Dec. 6, 1949 ELECTRICAL CONTACTING EIJLIVIEN'II"v- Franck.. Hensel and-EarlL Larsen, Indianapolis,

Intl.A assignorsto.. l.` It. Mallory & Co., Inc., Indianapolis` 1nd .a corporation of Delaware-y Application,I'ulye I9,r 1945, Serial No. 605,922

' 3 Claims. l This invention relatesA to electriealcontacting elements subject toV arcing.

An object of the invention isn toimprove elet-:-l tric contacts.. and electrodes.

Another object of the invention is toy improve` electrical make and break contacts, and electrodes, to produce. in such devices, due.-i to thev structural composition thereof, a. reduced elec trlcal. resistance, less tendency for arcing, pitting, transferring or tendency to weldor fuse during operation, less susceptibility to tarnishing and oxidation, and. the ability tooperate,in` an. ima` proved manner as` compared with electrical contacts. and electrodes commonly used. in the. same fields of application.

Otherobjects of the. invention will. be. apparentv from the description and claims..

Fig. 1 is` a plan, view of an, electrical. terminalI member embodying this invention', and

Fig. 2 is a side elevation. of the. structureel Fig. l.

Heretofore, electrical make and break contacts.

have been used in various applications, Ofjwhich,

the use as contactor contacts in an electrical` system may be taken as representative. Such contacts have been commonly made from .various metals and alloys thereof, such, as for example, copper, silver, copper-tungsten mixtures, silvertungsten mixtures, and the like. Upon breaking an electrical circuit by separating two contact points, arcing occurs between these contactsy which often gives rise to serious conditions materiaily affecting efficient.V operation thereof. Under the action of the rapid recurrence of the arcing, the faces of the contacts pit, fuseV and frequently weld together. ects are often accompanied yby the formation of undesirable compounds which increases the contact resistance and causes an undesirable temperature rise resulting ultimately in completeA failure of the contacts.

In our copending application Serial No. 463,118`

lerl October 23, 1942, now. Patent No. 2,396,101, issued. March 5, 19.46, we have,` disclosed a contact material formed from an alloy or mixturecon Such deleterious el?` The carbonatos which are particularly useful" are calcium carbonateL barium carlzonatc,` and. strontium carbonate yli'ecause their decomposltl'onl temperatures are above the temperatures which are. encountered.: in; inalnngfA sinteredv compactscontaining such carbonates..

While we do. notwisnto be.. limitedtherebr, it is,

believed that the improved results obtained with. the material of the present invention is due in part atv leastf to they tactv that therefractoryAA carbonateissnotmelted and vhence, when arr-aro is drawn and a..hi.s h.- temperatlire.Yisreached... carbonates prevent the flowing together ofthel silver to form a molten pool which would cause contact sticking, andatth'e same time,` thel gases4V releasedl Y by thevdecomposition l of the carbonatos'- to. oxides.. have are..vv extinguishing. character. These oxides, as derived from initially inserted; carloonates,y are-,verystable.1at high,- temperatures and will not `;deeoinpos.e -.faridiorm alloysgatthe.

temperatureof contactarcingi- When .using f the. carloonates;l they, are initiallyinserted. as. part otthe,` original composition. These. carbonatos decompose.Y to4 formv oxides.

during. the Contact operationand particulany` durinsarcng.

The relatively high electrical. conducting metal.- may loe-copper, silver, or. gold, `or copper, silver or.. gold basealloys andra carbonate of' one of the alkalineI earth metals. selectedimmthe grou consisting 015.1calcium.,4 strouttumandbarium.

The oxides of these metals, as derived, from initially inserted carbonates lare; characterized byl extremelyv high. melting: points., andA 'ai-very'.A high electricalv resistirity. The; oxides are. furtheh more very stable.. meltingrqoui'sof;Y the principal oxidescontemplated araasfollowsr Calcium oxide 2572. strontium oxide. -i Mn,... 24.30. Barium.. oxidenwvs .i-Mq

It can, therefore, bestated thatthe oxidesiresulting from decomposing carbonates which this in.,-

ventiori includes are characterized by a, melting.

to Welding or sticking, the respective proportions being given in per cent by weight.

Original compositions: Per cent Calcium carbonate 3 Silver 97 Barium carbonate 10 Silver 90 Strontium'carbonate -5 Silver 95 Calcium carbonate 3 Copper 97 Barium carbonate 10 Copper 90 Strontium carbonate 2 Copper 98 Intermediate compositions, in which part of the carbonates have decomposed to oxides:

- Percent Calcium carbonate and calcium oxide 3 Silver 97 Barium carbonate and barium oxide 10 Silver 90 Strontium carbonate and strontium oxide 5 si1ver 95 Calcium carbonate and calcium oxide 3 Copper 97 Barium carbonate and bariuml` oxide 10 Copper 90 strontium carbonate and strontium oxide 2 Copper; 98

The contact material may be formed by several different methods, for example:

(l) Finely divided particles ofthe relatively high electrical conductivity material are intimately mixed with nely divided particles of the carbonate material or a mixture of oxides and carbonates. The mixed particles or powders are subject to pressure to form the desired contact. The pressure may be increased to such a degree that porosity in the pressed contact is-materially reduced. The pressed piece may then be sintered in a suitable atmosphere, so as to bring about a bonding or fritting of the metallic particles to increase the strength of thefcontact. After this sintering operation, the contact may be re-pressed or hot worked or cold worked, to further increase the density, strength or other physical properties, after which it may again be subjected to a further sintering operation. It is possible to' carry out the sintering operation so that the carbonates will partly decomposev and the resulting compact consists of contact metal having interspersed therein a mixtulfv of carbonates and oxides.

(2) The mixed refractory and metal powders may be hot pressed, as for example, onto copper or a silver-plated copper backing ata temperatures sufficiently high to produce a bonded contact body.

In any. of the above processes and particularly that described under (2) above. it may be desirable in some cases to add a small proportion such as .01 to 2% of chlorides, vbromides and ioddes of silver and copper. I

In using Icarbonates in the initial composition care is preferablytaken lto avoid decomposition of the carbonates .to oxides duringthe forming-- of thecontact.- Sintering is carried out below the decomposition point of the particular car- 4 bonate being used and processing decomposition thus held to a negligible minimum.

For this purpose, carbonates of calcium, strontium and barium are preferred. Calcium carbonate decomposes at 825 C., strontium carbonate and barium carbonate at 1400 C. These gures represent the decomposition points in the absence of water.

In use, the walls of contacts of carbonate compositions as described decompose in arcing to create a vapor phase which provides the contact with improved non-sticking characteristics while retaining low contact resistance.

While specic embodiments of the invention have been described, for example, electrical make and break contacts, it is intended to cover the invention broadly within the spirit and scope of the appended claims, for example, to include any electrical contacting element and particularly those which are subject to arcing.

We claim:

1. An electrical make and break contact formed of a solid body having uniform composition throughout consisting of 1% to 10% by Weight of alkaline earth metal carbonates selected from the group consisting of the carbonates of calcium, strontium and barium, the balance being all silver, said contact having a very high resistance to Welding and sticking and said alkaline earthmetal carbonate minimizing arc formation through gases released by the decomposition thereof at Contact operating temperatures.

2. An electrical make and break contact formed of a solid body having uniform composition throughout consisting of 1% to 10% by Weight of calcium carbonate, the balance being all silver, said contact having a very high resistance to welding and sticking and said calcium carbonate minimizing arc formation through gases released by the decomposition thereof at contact operating temperatures.

3. An electrical make and break contact formed of a solid body having uniform composition throughout consisting of 3% by Weight of calcium carbonate and 97% by Weight of silver, said contact having a very high resistance to Welding and sticking and said calcium carbonate minimizing arc formation through gases released by the decomposition thereof at contact operating temperatures.

FRANZ R. HENSEL. EARL I. LARSEN.

REFERENCES CITED .The following references are of record in the file of this patent:

UNITED STATES PA'IENTS OTHER REFERENCES Hackh: Chemical Dictionary, 3rd edition,l

1944, by Grant` pages 631, 632; Blakiston Co.. Phila., Pa.).

(pub. by The 

